The present invention relates to moisture-curable silylated, i.e., silane end-capped, polymers, e.g., polyurethane prepolymers, possessing improved storage stability and to moisture-cured compositions obtained therefrom.
It is known to modify polymers, e.g., polyurethane prepolymers, by reaction with any of a variety of hydrolyzable organofunctional silanes. Moisture-curable silylated polymers, notably, silylated polyurethane prepolymers, have found widespread application as adhesives, sealants and coatings for which cure time and storage stability are important, even critical, functional properties.
Polymers silylated with silanes possessing trimethoxy groups exhibit desirable cure time and deep section cure. Methoxysilanes with reactive organofunctional groups have often been selected for use in silylating polymers. However, the moisture-curable silylated polymers can be difficult to process and often exhibit poor storage stability which manifests itself as an increase in the viscosity of the formulated adhesive, sealant or coating compositions containing them and often results in premature gelation and/or poor gunnability or sprayability of the compositions. Moisture-curable polymers containing only trimethoxysilyl groups react readily with ambient moisture that is present in many of the components used to formulate adhesive, sealant and coating compositions. Wetting agents, fillers, prepolymer, and the like, may contain amounts of absorbed and/or adsorbed water in quantities sufficient to result in premature gelation or viscosity increases even after storage for relatively short periods, e.g., days or a few weeks. In order to provide a storage-stable product, it is common practice to carefully dry each moisture-containing component of an adhesive, sealant or coating composition containing a moisture-curable silylated resin, mixing the components under moisture-free conditions and storing the composition in a suitably dry environment. However, mixers require special equipment to provide for an inert atmosphere. The use of thoroughly dried components and the special handling required during production of the aforesaid adhesives, sealants and coating compositions adds cost to their manufacture and may still result in unusable products due to premature gelation and/or poor gunnability or sprayability. While moisture-curable silylated polymers that contain alkoxysilyl groups wherein the alkoxy groups have two or more carbon atoms provide for good storage-stability, they generally exhibit poor cure times and poor deep section cures even when large amounts of hydrolysis and condensation catalysts are included in the fully formulated compositions.